Method for powdered metal forming



T. E PIPER ETAL 3,377,164

April 9, 1968 METHOD FOR POWDERED METAL FORMING Filed Jan. '7 25, 1965 2Sheets-Sheet 1 ,fl-IOMAS =61 WLsaA/JQQQQW;

April 1968 i. E. PIPER E 3,377,164

METHOD FOR POWDERED METAL FORMING 2 Sheets-Sheet 2.

Filed Jan. 25, 1965 Y s. 2 a Q P P. E o o 0 k I M w m EN S mw fiwxcwwumgvflw nmwhm Sw m WW I A I... E: W\QMQQIM \QKQKQRV W S V, II I. I I wwwfilUnited States Patent 3,377,164 METHOD FOR POWDERED METAL FORMING ThomasE. Piper, La Julia, and Wilson N. Pratt, Anaheim, Calif., assignors toGeneral Dynamics Corporation, Pomona, Califi, a corporation of DelawareFiled Jan. 25, 1965, Ser. No. 427,665 13 Claims. (Cl. 75-214) ABSTRACTOF THE DISCLQSURE Broadly, the method of the disclosure consists ofmixing the desired ratio of metal powders, pressing the mixture of metalpowders to form a briquette, heating the briquette to the plasticcondition of the metals, inserting the heated briquette in a die of adesired configuration, forming the heated briquette to the dieconfiguration by striking same with a high energy rate means, andremoving the formed article from the die. The apparatus for carrying outthe method may be manually or automatically operated.

This invention relates to the forming of metal parts, particularly tothe forming ,of parts utilizing metal powder, and more particularly to amethod and apparatus for making three dimensional parts by high energyrate forming of metal powder.

It has heretofore been the usual practice to form three dimensionalparts from stock by machining operations which involve the removal of asubstantial amount of metal in the defining of geometrical features ofthe part. This procedure is not only wasteful of material but is alsotime consuming and accordingly, expensive.

High performance missiles, spacecraft and aircraft require the ultimatein structural part design and fabrication. Designers can envisageoptimum systems and parts, but are forced by technological limitationsto compromise their designs of parts and systems to compensate forproducibility aspects.

This invention is directed to a process,and apparatus for carrying outthe process, which forms precision metal alloy parts directly from metalpowders by a high energy rate force and thus greatly advances the knowntechnology. This process is capable of consistently and rapidlyproducing substantially finished, high quality parts of a wide varietyof shapes and sizes, in one ope-ration. This process is extremelyeconomical. In addition to effecting a high production rate, the processis not limited by processing characteristics of exotic alloys. Becausethe raw material for parts produced by this process is low cost metalpowder, new metal alloys may be formulated as required to meet themechanical, physical and environmental perfiormance requirements, beyondthe present state of the art.

In the process of this invention metal powders are mixed to give thealloy desired, and compacted into a briquette. After compaction, thebriquette is heated in a controlled atmosphere to the plastic range.This temperature is normally below the solidus. After the briqette is atthe plastic range, it is formed in a die with high energy rate forces.This may be done, if desirable, in the presence of an inert gas.

The high energy rate extrusion process of the present invention producesseveral unique results. The part is formd in the precise shape of thedie with complete filling of the die. Flow lines are eliminated,resulting in a maximum longitudinal strength of the material With noreduction of strength in the transverse direction. The extrusion processalso gives excellent grain refinement with superior metallurgical andphysical properties.

I The present process depends on the ability of a porous body (billet orbriquette) of heated metal (metal powder) to be deformed by extrusion ina three dimensional die using a high energy rate forming apparatus. Thehigh energy rate is necessary to minimize temperature loss during theprocess and to insure plasticity. Thus, the process produces a highdensity part from a low density metal powder billet.

An aerodynamic surface, such as a control surface of a missile, can beformed by the present invention by using only about half of the energynecessary to extrude the same shape from a bar of solid metal, therebyincreasing the life of the tooling utilized. Additionally, articlesformed from metal powders in accordance with this invention have a grainstructure different than that of articles formed from solid metal. Thisis due to the high velocity of the individual particles being achievedwith a small energy loss as compared with energy losses associated withhandling a massive piece of solid metal, because the interstices betwenthe powder particles offer voids for deformation and paths for flow andwill accelerate as fast as the metal powder particles and be deformedonly through deformation of the metal powder particles caused by backpressure. It has been determined that by a careful manipulation ofenergy rate application, proper control of the density of the preformedbriquette, and control of the plasticity of the metal powder particlesthrough temperature regulation, a nearly or completely dense body can beproduced in a shaped die, the term dense inferring specific gravity. Thepart thus produced requires a minimum of machining as a secondaryoperation. The tooling (apparatus) is not unnecessarily stressed whichinsures long life. The resulting parts have unusual properties beingcharacterized primarily by small grain size. Thus, with the process ofthe invention, metallurgical compositions can be produced that are notpossible to cast, etc.

Therefore, it is an object of this invention to provide a method andapparatus for forming metal parts.

A further object of the invention is to provide a method for formingpartsfrom metal powders.

Another object of the invention is to provide a method for forming threedimensional parts from metal powders utilizing a high energy rateforming apparatus.

Another object of the invention is to provide a method for producing ahigh density part from a low density metal powder billet.

Another object of the invention is to provide a method of making threedimensional parts from metal powders wherein the parts have asubstantially uniform fine grain structure.

Another object of the invention is to provide an apparatus for heating,transferring, and forming by high energy rate application, metal powdersinto substantially finished parts.

Other objects of the invention, not specifically set forth above, willbecome readily apparent from the following description and accompanyingdrawings wherein:

1 FIG. 1 is a plan view illustrating a three dimensional articleproduced by the invention;

.FIG. 2 is a view taken on line 22 of FIG. 1;

FIG. 3 is a schematic view illustrating compaction of the powder metalbriquette;

FIG. 4 is a schematicview illustrating heating and extruding of thebriquette in a high energy rate forming apparatus; and

FIG. 5 is a view illustrating an embodiment of an apparatus for carryingout the method of the invention.

Referring now to the drawings, FIGS. 1 and 2 illustrate a threedimensional article formed in accordance with the invention, thearticle, for illustration purposes only, being an aerodynamic surface 10for an air vehicle or the like which, prior to this invention as setforth above, had to be machined from stock material. Aerodynamic surfacecomprises a butt or base portion 11 and a contoured an apex 17. Bodyportion 12 additionally includes a fiat surfaces 13 and 14. Surface 13is inclined from a leading edge 15 rearwardly, with surface 14 beinginclined from a trailing edge 16 forwardly to intersect with 13 todefine an apex 17. Body portion 12 additionally includes a flat bottomsurface 18 and an outboard edge or tip 19 which is perpendicular withrespect to the leading and trailing edges 15 and 16. Body portion 12tapers as indicated at 20 from trailing edge 15 to butt portion 11. Alsoapex 17 curves rearwardly at and abuts the tapered area 20.

FIGS. 1 and 2 thus clearly illustrate the problems involved and themachining requirements to make articles such as aerodynamic surfaces 10or other three dimensional articles by prior known methods. Sucharticles are quickly and economically made by the method and apparatusof this invention.

There are many known methods of producing metallic powders usable in thepresent invention. For example,

when a steel such as SAE 4600 is melted and poured in thin streams by across jet of liquid, such as water, the liquid steel is broken into verysmall drops which solidify almost instantly because of their highsurface area-to-rnass ratio and the quenching effect of the jet. Theparticles made in this way are dried and annealed in a furnacecontaining a reducing atmosphere. The resulting powder contains verylittle oxide, is decarburized and each particle is, in effect, a verysmall solid ingot. The absence of carbon is important because theferritic powder produced is sufficiently soft to mold into billets orbriquettes at a comparatively low pressure. Many alloy steels can bemade using this method. The size of the powder particles normally isdirectly related to the grain structure of the formed article.

An alloy powder, such as taining nickel and molybdenum, both of whichwill reduce easily is preferable because it can be made with a very lowoxide content. A typical chemical analysis of this powder is as follows:

Carbon 0.01 Silicon 0.26 Manganese 0.49 Sulfur 0.04 Phosphorus 0.012Nickel 1.86 Molybdenum 0.28 "Iron Balance The typical physicalproperties of this powder are as follows:

Sieve analysis, mesh percent:

100 0.2 100-140 12.5 140-200 24.1 200-325 35.7 325 27.5 Approximatedensity gms./cc 3.21 Flow(sec./50 gms.) 22

SAE 4600 metal powder 99.3 Zinc stearate 0.5 Graphite 0.2

The mixing container can be, for example, placed on rollers and rolledat a speed which causes the powder to cascade. The powder is mixed withthe additives until satisfactory heterogeneity of the constituents isproduced.

SAE 4600, for example, con- Other methods of mixing the powder, such asa twin shell dry blender, may be effectively utilized.

The billet or briquette 30 is produced in a die 31 with a bottom and atop punch 32 and 33, respectively, as schematically illustrated in FIG.3. The diameter of die 31 is determined by the size of the billet 30required to form a specific article; thus various size dies oradjustable dies are required. The punches 32 and 33 have very closetolerances with respect to the internal diameter of the die 31. Thepunch and die assembly, as here illustrated by way of example only, isset up to provide double action pressing which produces a billet with asuniform a density as possible. The density, for example, of SAE 4600metal powder mixture, may be maintained at 6.2 to 6.4 gm./ cc.

The steps in producing a billet 0r briquette 30 will vary depending onthe equipment being utilized. Briefly, with a double punch and dieassembly as illustrated in FIG. 3, the steps include:

The briquettes or billets are produced without heating sintering) sinceit is desirable to maintain interstices between the powder particleswhich offer voids for deformation and paths for flow of the particles.This produces the fine grain structure in the formed article.

With a billet or briquette 30 formed by pressing as described above orby other forming methods such as by an automatic tableting (billet)machine, the aerodynamic surface 10 or other three dimensional articleis formed from the billet 30 in a high energy rate forming (H.E.R.F.)apparatus such as that commercially known as Dynapak and manufactured bythe assignee of this application and described, for example, in US.Patents 2,925,803; 3,036,- 538 and 3,093,117. H.E.R.F. apparatus asdefined herein is a forming apparatus which utilizes a high energy powersource for driving the ram unit thereof at a high velocity rate. Forexample, the energy used to form the surfaces illustrated in FIGS. 1 and2 is approximately 14,300 foot pounds applied to the heated metal powerbillet at a velocity of 760 ft./sec. The larger the part being formed,the higher the required pressure, and higher pressures require highervelocities where the mass of the ram is constant. Thus, with varioustypes of forming apparatus and/or various types of parts being formed,the energy will vary, and it is the energy applied over a certain periodof time which produces the grain structure of the formed article. Thevelocity of the ram unit of the apparatus is important because of itsbeing a square function as illustrated by the formulas E=WV /2G or E=MVin which:

E=energy W=weight V: velocity G: gravity M =mass The forming operationof a billet 30 into a three dimensional article such as aerodynamicsurface 10 is illustrated in FIG. 4 and consists essentially of fouroperations; namely, heating the billet, transferring the heated billetto the die of the H.E.R.F. apparatus, forming the article by actuating(firing) the H.E.R.F. apparatus, and removing the formed article.

The billet or briquette 30, formed as described above, is heated in afurnace, indicated at 40, supplied with an atmosphere supplied by anendothermic gas generator because the billet 30 contains carbon, and acarbon potential must be maintained in the protective atmosphere.

Heating a metal powder preform necessitates the control of threevariables: time, temperature, and atmosphere.

Time for heating depends on four variables which are heat conductivity,size, temperature, and alloy changes desired.

The heat conductivity is important. Copper, for example, heats muchfaster than bronze or steel. Time is thus related to this factor. It iscalled thermal conductivity, because this factor is usually expressed ask in B.t.u./hr. sq. ft./F./ft. The higher the number, the faster themetal will heat. The k value for copper at 212 F. is 218 while that ofsteel at 212 F. is 26. Roughly copper willheat 8 times faster thansteel.

The size of the billet is important because it takes longer to heat alarge billet than a small billet of comparable shape. Thus the area ofheat input is important. The heating of any body follows the followinggeneral formula AT [CAT in which:

k=thermal conductivity (factor) A=Area AT=temperature differential x==average dimension divided by 2.

From the above it is obvious that in the heating of the center of thebillet to furnace temperature, time would become infinite because of thetemperature differential approaches zero g becomes much smaller.

More time will be necessary to heat the billet to a high temperaturethan a low temperature. This is because more B.t.u. input is requiredand also because on metals the k factor is reduced with increasingtemperature.

Alloy changes may or may not take times longer than heating time. Thisdepends on the change necessary. In the article illustrated carbon isdiffused into the iron base alloy to produce steel. If chromium werepresent as an alloying element, more time would be necessary becausethis element slows down carbon solution. If solution of metastableintermetallics such as are cip-itation hardening alloys (17-4 ph) arenecessary, then more time may be needed.

Time is usually determined experimentally and the shortest possible timeis used but time can vary considerably. The examples quoted above areonly a few of the considerations made in deciding what time to use inheating a metal powder billet.

Temperature is important because it produces the plastic alloy state(low elastic limit) which allows the process to produce shaped parts. Itmay be possible to form parts above the solidus but tool trouble andalloy heterogenity would be expected. If the plastic range is verynarrow this process will still work because of speed. It is normal informing to heat as high as possible without melting any of theconstituents or causing excessive grain growth. Some times heating totoo high a temperature will cause migration of some'of the alloyconstituents (carbides in grain boundaries of 18-4-1) and may beextremely detrimental. The temperature selected is a matter ofexperience and good metallurgical practice. It is possible to extrudealloy powders of an analysis which can not be forged as cast.

The study of atmospheres is in reality the study of the interaction ofgas and metallic surfaces. Metal powders have very large surface areascompared to their mass.

found in preables and the values assigned them,

The interaction of gas and the large surface area, which is chemical innature, is thus of the utmost importance. Atmospheres react in variousways with metals dependent on the chemical content of the gas and theposition of the metal in the electro motive series of elements.Aluminum, silicon, manganese, chromium all lie above hydrogen andtherefore, produce very stable oxides. If these metals are a majorconstituent in an alloy such as 304 stainless steel (18% chromium) thenthe formation of oxides should be avoided. If no oxygen is present inthe protective atmosphere then very little oxide can be formed. Heatingin a vacuum, dry inert gas, dry hydrogen, or disassociated anhydrousammonia in a very tight system will result in a low oxide content billetsuch as is necessary for austenitic stainless steel or other chemicallyactive alloys.

Endothermic atmospheres produced by reforming hydrocarbons and theoxygen in the air can be made to produce gas with a carbon potential.Endothermic gas is used as a means of controlling the carbon content inthe surface of steel. The gas carbon potential is due to the presence ofcarbon monoxide and the amount of carbon monoxide may be changed bychanging the mixture of gas and air fed to the heated catalytic chamber.The ratio between carbon monoxide, carbon dioxide, and water vapor is aconstant for any single temperature and because the water vapor contentis easily checked, it has become practice to describe the carbonmonoxide content (carbon potential) as dew point.

New systems of carbon dioxide measurement such as by infrared cellsoffer advantages over the prior known methods. Roughly the carbonpotential is inversely proportional to the dew point and is proportionalto the temperature and carbon content. The selection of carbon potentialis dependent on temperature and carbon in the steel. It is possible tocarburize steel using endothermic atmosphere and possible to decarburizesteel using an endothermic atmosphere; therefore the selection of theproper dew point is important and a variable. Endothermic atmospheresare not suitable for chemically active alloys because of their watervapor and carbon dioxide content and because they will carburize somealloys such as 18-8 stainless steel.

Exothermic atmospheres are simple products of combustion of hydrocarbongas and air. Exogas is useful in protecting bronze s, iron, etc., at lowtemperatures. The easily reducible copper base alloys, with theexception of zinc containing brass, can be heated with confidence inthese atmospheres.

Thus, variations in time, temperature and atmosphere depend onconditions pertinent to each system and can be solved only by experienceand at best can be controlled accurately only by constant surveillance.

As pointed out above, the variations in the heating process or operationare three. Following is a list of these variby way of example only, forthe production of an article such as aerodynamic surface 10 from SAE4600 metal powder mixture:

Atmosphere Endothermi-c 10 F. Dew Point. Temperature 2300 F. Time 20minutes in the furnace.

During the heating cycle, several changes take place. The graphite goesinto solution in the ferrite producing iron carbide which at thediffusion temperature also remains in solution. The zinc stearate isvolatilized from the billet and no trace of zinc is found onspectographic analysis of the finished article or part.

The billet 30, heated to the plastic state in furnace 40, is transferredas indicated by the arrows and legend in FIG. 4 to the lubricated andassembled tooling set up (H.E.R.F. apparatus) generally indicated at 41.Transfer time varies from 3 to 5 seconds, depending on the method oftransfer utilized. Apparatus 41 as schematically illustrated in FIG. 4comprises a receiver unit 42 for the heated billet 30, a power unit 43having a ram 44 which moves through receiver unit 42 into a die block45. Die block 45 retains therein a split die 46 configured to define theshape of the formed article or part, block 45 including an aperture 47which serves as an exhaust port thereby preventing an internal explosionin the die 46 due to the forces therein. If desired the die 46 mayinclude an orifice 48 through which the billet material is extrudedprior to its entry into die cavity 49. The heated billet having beenpositioned adjacent die 46 and with the power unit 43 of the H.E.R.F.apparatus 41 set at a fire pressure, for example, at 400 p.s.i., with aback pressure, for example, of 100 p.s.i., the power unit is activatedand the heated billet is forced at a high velocity into die cavity 4-9by the rapid movement of ram 44, the billet thereby conforming to theconfiguration of die 46. The split die 46 is then removed from die blockand the formed article or part 10 is removed from the die. The averagetravel distance of ram 44 is approximately 7 inches. This distance willvary depending upon the high energy rate forming apparatus being used.

In tests conducted on articles such as aerodynamic surface 10 made fromthe above stated metal powder mixture and in accordance with theinvention, final chemical analysis of the high energy rate formedarticle was as follows:

Carbon 0.20 Nickel 1.83 Manganese .50 Silicon 0.35 Molybdenum 0.27 IronBalance Hardness tests were made of the thus formed aerodynamic surface16. The hardness averages about an RC 23, with near an RC 45 over theflat body portion 12 and about an RC 10 at the heavy butt portion 11.

The microstructure of samples of articles produced by this invention isunusual. The small particle size of the raw material, which is notconsolidated until the end of the forming operation, results in a finegrain equi-axed structure. The variations in the movement of the metalduring the extrusion process result in a variation in microstructurethroughout the article produced.

It has thus been shown that this invention will extrude low carbon steelfrom powders at very low forming (firing) pressures. The metallurgyinvolved is unusual but the fine grain structure in the blade or bodyportion of surface 10 and the unusually high hardness when even smallamounts of carbon are added produces structural integrity. The uniformlyhigh density and the absence of porosity in the blade indicate that themodules will be the same as steel produced by conventional methods.These novel results are due to the use of metal powders formed into anend article by a high energy rate forming apparatus, which due to thehigh rate at which the heated billet material is extruded, cannot beproduced by any prior known process.

Referring now to FIG. 5, the embodiment of a mechanism for carrying outthe forming process includes a high energy rate forming apparatusgenerally comprised of a hydraulic power supply unit 50, a power unit51, a control console 52, and an induction heating power supply unit 53.

Power unit 51 includes a die support mechanism 54 mounted on supportmembers 55 and a ram 56 movable along support members 55. Operativelymounted in die support mechanism 54 is a tapered die holder or block 57within which a split die 58 is positioned, die 58 being configured todefine the shape of aerodynamic surface 10 or other three dimensionalarticles or parts. A die ejection cylinder 59 is operatively supportedby mechanism 54 and functions to move split die 58 into or out of holderor block 57. Cylinder 59 is connected with a pressure source (not shown)through conduits 60 and 61.

Induction heating power supply unit 53 includes an atmosphere controlledheating tube or tunnel 62 for billets 30 having a loading chute 63 and agate 64 controlled by an escapement mechanism 65, such as a solenoid. Aloading ramp or chute 66 is pivotally mounted adjacent gate 64 and israised or lowered by means (not shown) through arm and lever mechanism67. A billet inserting mechanism 68, such as a solenoid, is mounted atthe end of ramp 66 and functions to insert a billet 30 into split die58.

In operation of the embodiment of the apparatus illustrated in FIG. 5for carrying out the forming process of the invention, billets 30prepared by pressing from powdered metals as described above areinserted at proper sequence into heating tube or tunnel 62 and heatedunder controlled environment for the required time. When a billet 30 isheated, loading ramp 66 is lowered to the solid line position,escapement mechanism 65 is actuated to open gate 64 and allows a billet30 to roll to the end of ramp 66 which is aligned with the opening insplit die 58. Actuation of billet inserting mechanism 68 inserts heatedbillet 30 into die 58. Loading ramp 66 is retracted to the positionshown in phantom. Power unit 51 is actuated, which fires ram 56 againstbillet 30 which extrudes the billet material to the configuration of thesplit die cavity. As described above, power unit 51 includes means forretracting ram 56 after firing. Die ejection cylinder 59 is actuatedwhich causes split die 58 to move out of tapered block 57 and open. Theextruded article is removed, the die lubricated and cylinder 59retracted thereby securing split die 58 in tapered holder or block 57and placing the apparatus in condition for repeating the cycle.

While not shown, the control functions of the FIG. 5 mechanism may beelectrically interlocked to provide rapid foolproof cycling or may beindependently operated as shown.

It has been shown that the preforming and heating of a billet can becontrolled to permit rather extensive and easy extrusion of relativelythick and thin sections by high energy rate forming apparatus. Anotherdesirable feature of extruding a preformed powder metal billet hereinprovided is the ease of compounding new compositions to a high degree ofreproducibility to provide the desired flexibility of modification ofchemical composition, hardenability and physical properties, if changesin design conditions so demand. An additional beneficial feature of thepresent inventive technique is revealed in the extremely fine grainstructure that can be developed in the formed parts. It has been shownthat practical theoretical density can be obtained following impactextrusion of relatively thick and thin sections using the high energyrate forming apparatus, thus providing substantially complete absence ofresidual porosity, this being accomplished by appropriate gating andventing of the die cavity.

Following impact extrusion, and as indicated above, a very fine grainsize is developed utilizing the present invention, resulting in a veryfine structure in the asextruded and cooled part. The grain size isextremely fine in the thinnest sections (0.012" thick) and yet muchfiner than usual for wrought steels in thicker section (0.250 thick).Thus good toughness can be obtained in dense extruded sections.

Tests have shown that the alloy compositions that are common inconventional alloying techniques can be formed by the present invention.Thus, for example, it is possible to produce parts from 20% tungstenadditions as easily as working with steel. However, tool and diematerials, die lubricants, oxidation inhibitors in powdered metalmixtures, etc., present problems which have to be considered for thevarious types of powdered metal mixtures being formed.

Advantages of the forming method and apparatus of this invention aresummarized as follows:

(1) Low raw material cost in addition to very low formmg costs.

(2) Articles from a Wide variety of alloy combinations can be produced.

(3) Superior physical properties of the formed article with nodirectional characteristics.

(4) Little or no machining of the formed article required.

(5) Substantially no porosity in the formed article.

(6) A wide variety of article shapes can be made with very highprecision.

(7) Makes possible a high production rate.

Although a specific embodiment of the apparatus for carrying out theinventive forming process has been illustrated and described andspecific examples of materials and process conditions have been setforth as exemplifying the invention, modifications and changes willbecome apparent to :those skilled in the :art, and it is intended tocover in the appended claims all such modifications and changes as comewithin the true spirit and scope of the invention.

What we claim is:

1. A method for producing parts comprising the steps of forming a billetof predetermined powdered material, heating the formed billet to theplastic range thereof, positioning the heated billet in a die having apredetermined internal configuration, extruding the heated billet toconform with the internal die configuration by striking the billet witha high energy rate means, and removing the thus formed part from thedie.

2. The method of forming briquettes made of powdered metals into threedimensional articles comprising the steps of heating the briquette underpredetermined atmospheric and temperature conditions for a predeterminedtime, transferring the heated briquette to a die having an internalconfiguration for shaping the article to be formed, extruding the heatedbriquette to assume the internal configuration of the die by strikingthe briquette one time with a high energy rate forming apparatus capableof applying a predetermined amount of energy at a predetermined rate,and removing the formed article from the die.

3. The method defined in claim 2, wherein the atmospheric condition forheating the briquettes is a protective atmosphere for the type of metalpowder of which the briquettes are constituted.

4. The method defined in claim 3, wherein the protective atmosphere isan endothermic dew point range of 7 to 13 F.

5. The method defined in claim 2, wherein the temperature condition forheating the briquettes is below the solidus temperature.

6. The method defined in claim 2, wherein the temperature condition forheating the briquettes is in the range from 2200 to 2400 F.

7. The method defined in claim 2, wherein the heating time for thebriquettes is sufficient for diffusion of the briquette material.

8. The method defined in claim 2, wherein the heating time for thebriquettes is in the range from 15 to 25 minutes.

9. The method defined in claim 2, wherein the energy of the high energyrate forming apparatus is applied at a velocity above 700 feet persecond.

10. The method defined in claim 2, wherein the briquette is composedessentially of carbon, silicon, manganese, sulfur, phosphorus, nickel,molybdenum and iron, and wherein the briquette is heated for a timeperiod in the range from about 15 to 25 minutes to a temperature in therange between about 2200 F. and about 2400 F. under an endothermic dewpoint range of about 7 F. to about 13 F.

11. The method defined in claim 10, wherein the heated briquette isextruded by the high energy rate forming apparatus being applied at avelocity above 700 feet per second.

12. The method defined in claim 2, wherein the heated briquette isextruded by the energy of the high energy rate forming apparatus beingapplied at a pressure in the range from about 300 p.s.i. to about 700p.s.i. and at a velocity in the range from about 700 feet per second toabout 900 feet per second.

13. The method defined in claim 2, wherein the briquette is selectedfrom the group consisting of steel. copper, aluminum and stainlesssteel.

References Cited UNITED STATES PATENTS 2,359,013 9/1944 Tucker 2643292,669,764 2/1954 Kilpatrick 264329 2,794,241 6/1957 Dodds -214 X2,928,733 3/1960 Wagner 75-222 X 3,155,502 11/1964 Brown 75214 3,165,5701/1965 Deutsch 264329 FOREIGN PATENTS 686,673 5/ 1964 Canada.

443,703 2/ 1936 Great Britain.

781,083 8/1957 Great Britain.

OTHER REFERENCES Goetzel, Treatise on Powder Metallurgy, Vol. I, 1949,Interscience Publishers, N.Y., pp. 3 and 424-426.

CARL D. QUARFORTH, Primary Examiner. BENJAMIN R. PADGETT, Examiner. A.J. STEINER, Assistant Examiner.

